Move check from sema to parse, closes #712

Semantic checks for things the user shouldn't be able to write even as input to a metafunction can be done early, in `parse`

Other semantic checks go in `sema` so that metafunctions have more liberty to take otherwise-incomplete definitions and complete them with the metafunction's own defaults (or do things like remove a member and replace it with something else that is complete)

Author: hsutter

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.2.1   Build 8928:1358
+cppfront compiler v0.2.1   Build 8930:0819
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

source/build.info

@@ -1 +1 @@
-"8928:1431"
+"8930:0819"

source/parse.h

@@ -7981,6 +7981,23 @@ class parser
             }
         }
 
+        //  A type initializer must be a compound expression
+        if (
+            n->is_type()
+            && !is_parameter
+            && (
+                !n->initializer
+                || !n->initializer->is_compound()
+                )
+            )
+        {
+            errors.emplace_back(
+                n->position(),
+                "a user-defined type initializer must be a compound-expression consisting of declarations"
+            );
+            return {};
+        }
+
         //  If this is a type with metafunctions, apply those
         if (n->is_type()) {
             if (!apply_type_metafunctions(*n)) {

source/reflect.h

@@ -937,7 +937,7 @@ declaration_base::declaration_base(declaration_base const& that)
     auto declaration::mark_for_removal_from_enclosing_type() & -> void
 
     {
-        cpp2::Default.expects(parent_is_type(), "");
+        cpp2::Type.expects(parent_is_type(), "");
 #line 285 "reflect.h2"
         auto test {CPP2_UFCS_0(type_member_mark_for_removal, (*cpp2::assert_not_null(n)))}; 
         cpp2::Default.expects(std::move(test), ""); // ... to ensure this assert is true

source/reflect.h2

@@ -280,7 +280,7 @@ declaration: @polymorphic_base @copyable type =
     parent_is_polymorphic: (this) -> bool = n*.parent_is_polymorphic();
 
     mark_for_removal_from_enclosing_type: (inout this) 
-        [[pre: parent_is_type()]]                   // this precondition should be sufficient ...
+        [[pre Type: parent_is_type()]]              // this precondition should be sufficient ...
     = {
         test := n*.type_member_mark_for_removal();
         [[assert: test]]                            // ... to ensure this assert is true

source/sema.h

@@ -1031,20 +1031,6 @@ class sema
             return false;
         }
 
-        //  A type initializer must be a compound expression
-        if (
-            n.is_type()
-            && n.initializer
-            && !n.initializer->is_compound()
-            )
-        {
-            errors.emplace_back(
-                n.position(),
-                "a user-defined type initializer must be a compound-expression consisting of declarations"
-            );
-            return false;
-        }
-
         //  A namespace must be initialized with a compound expression
         if (
             n.is_namespace()